The invention relates to a process for the preparation of functionalized alkoxyamine initiators and to their use in radical polymerization.
A one-pot process for the preparation of functional alkoxyamines of the general formula (I), 
is disclosed. The process entails (1) reacting an oxidizing agent with a sterically hindered secondary amine to produce an aqueous phase and a nitroxy radical (2) removing the aqueous phase and adding to the nitroxy radical one or more vinyl monomer(s) conforming to a formula and a system which produces free radicals. Also disclosed is a process of polymerizing monomers using the functional alkoxyamine.
The use of the controlled radical polymerization (xe2x80x9cCRPxe2x80x9d) of vinyl monomers has increased rapidly because it allows the synthesis of a broad range of well-defined (co)polymers under uncomplicated experimental conditions. The polymerization may, for example, be carried out in aqueous media and under moderate polymerization temperatures and purification of the monomer prior to polymerization is not required. Additionally, the main molecular parameters of the polymer chain, for example its polydispersity, molecular weight, polymer architecture or the structure of the chain-ends may be easily controlled and adjusted. The CRP is also called xe2x80x9clivingxe2x80x9d free radical polymerization. The aim of the precise control of free radical polymerization is achieved by reversible chain termination or blocking (xe2x80x9cend-cappingxe2x80x9d) after each growth step. The equilibrium concentration of the polymerization-active (xe2x80x9clivingxe2x80x9d) chain ends in this case is so low compared with the equilibrium concentration of the blocked (xe2x80x9cdormantxe2x80x9d) chain ends that irreversible termination and transfer reactions are greatly suppressed compared with the growth reaction. Since the end-capping proceeds reversibly, all the chain ends remain xe2x80x9clivingxe2x80x9d if no termination reagent is present. This allows the control of the molecular weight, low polydispersity and controlled functionalization of the chain ends by termination reagents.
Of all the CRP systems presently under investigation, the nitroxyl-mediated polymerization (xe2x80x9cNMPxe2x80x9d) is one of the most attractive and efficient, because this technique provides advantages applicable to a broad range of monomers such as (meth)acrylates, acrylonitrile, styrenes, acrylamides, butadiene or isoprene and may be carried out in a metal-free, colorless and odorless manner.
Numerous publications have shown that alkoxyamines may be used to initiate and control the radical polymerization of vinyl monomers according to an NMP mechanism.
U.S. Pat. No. 4,581,429 discloses alkoxyamines which are formed by the reaction of linear or cyclic nitroxides, such as 2,2,6,6-tetra-methylpiperidin-1-oxyl (TEMPO) with organic carbon-based free radicals, and a process for the preparation of vinyl polymers using these compounds as initiators. The reactions typically have a low concentration of free radicals which, in the free radical polymerization of vinyl monomers, means that bimolecular termination reactions are less likely to occur than unimolecular growth reactions.
Other examples are described by Hawker et al. (J. Am. Chem. Soc. 1994, 116, 11185 and J Am. Chem. Soc. 1999, 121, 3904-3920) and in U.S. Pat. No. 5,322,912, U.S. Pat. No. 5,412,047, U.S. Pat. No. 5,449,724, U.S. Pat. No. 5,498,679, U.S. Pat. No. 6,258,911, DE-A 199 09 767 and EP-A 0 891 986.
The most commonly used method for the synthesis of alkoxyamines consists in coupling an alkyl radical to a nitroxyl radical. The alkyl radical R0 may be generated by different methods, for example by decomposition of azo compounds (Hawker et al., Macromolecules 1996, 29, 5245-5254; Yozu Miura et al., Macromolecules 1998, 31, 6727-6729), by hydrogen removal from an appropriate substrate (Hawker et al., Macromolecules 1996, 29, 5245-5254; Yozu Miura et al., Macromolecules 1998, 31, 4659-4661) or by addition of a radical to an olefin (Hawker et al., J. Am. Chem. Soc. 1994, 116, 11185). The alkyl radical may also be generated from an halogenated compound Rxe2x80x94X in the presence of a metallic catalyst following an atom transfer radical addition (xe2x80x9cATRAxe2x80x9d) reaction (WO-A 00/49027; WO-A 00/61544).
EP-A 1 083 169 discloses a process for the preparation of functionalized alkoxy-amine initiators in which hydrogen peroxide is reacted with iron(II) sulfate in the presence of a nitroxyl radical and a vinyl monomer to form the alkoxyamine with a good yield in a one-pot process.
The major disadvantage of the methods described above is that the alkoxyamines have to be synthesised from costly nitroxyl radicals and generally must be purified before they may be used for polymerization.
The object of the present invention was to provide a new synthetic pathway for the synthesis of alkoxyamines in a one-pot process and to use these alkoxyamines as intermediates in a polymerization process which provides homo- and copolymers of narrow polydispersity with a specific molecular weight and which does not have the above-mentioned disadvantages of the prior art.
Surprisingly, it has now been found that hydroxy-functional alkoxyamines may be produced from secondary amines in a one-pot process and used, without intermediate purification, in a controlled, free-radical polymerisation process.
The object of the present invention is a one-pot process for the preparation of functional alkoxyamines of the general formula (I) 
wherein
R1, R2, R3 are independently selected from the group consisting of: hydrogen, C1-C20alkyl, C1-C20cycloalkyl, C6-C24aryl, halogen, cyano, C1-C20alkylester C1-C20cycloalkylester, C1-C20alkylamide, C1-C20cycloalkylamide C6-C24-arylester and C6-C24-arylamide;
R4 and R5 are independently selected from the group consisting of: C1-C18alkyl, C2-C18alkenyl, C2-C18alkynyl, C3-C12cycloalkyl, C3-C12heterocycloalkyl, and C6-C24-aryl, all of which are optionally substituted by NO2, halogen, amino, hydroxy, cyano, carboxy, ketone, C1-C4alkoxy, C1-C4alkylthio, C1-C4alkylamino; or
R4 and R5 form, together with the nitrogen atom linking them, a C3-C12cycloalkyl radical, a (C4-C12alkanol)yl radical or a C2-C13-heterocycloalkyl radical containing oxygen, sulfur or nitrogen atoms; or
R4 and R5 together form a residue of a polycyclic ring system or a polycyclic heterocycloaliphatic ring system containing oxygen, sulfur or nitrogen atoms;
wherein the carbon atom of the R4 and R5 radicals directly adjacent to the alkoxyamine nitrogen atom is in each case substituted by 3 further organic substituents and
wherein optionally at least one of the radicals R4 and R5 contains a functional group Y which is capable of further reacting or crosslinking with the functional groups known from the coatings field;
comprising the reaction steps of
(1) reacting of an oxidizing agent (A) with a sterically hindered secondary amine of the general formula (II), 
xe2x80x83wherein
R4 and R5 are independently selected from the group consisting of: C1-C18alkyl, C2-C18-alkenyl, C2-C18alkynyl, C3-C12cyclo-alkyl or C3-C12-heterocycloalkyl, C6-C24aryl, all of which are optionally substituted by NO2, halogen, amino, hydroxy, cyano, carboxy, ketone, C1-C4alkoxy, C1-C4alkylthio, C1-C4alkylamino; or
R4 and R5 form, together with the nitrogen atom linking them, a C3-C12cycloalkyl radical, a (C4-C12alkanol)yl radical or a C2-C13heterocycloalkyl radical containing oxygen, sulfur or nitrogen atoms; or
R4 and R5 together form a residue of a polycyclic ring system or a polycyclic heterocycloaliphatic ring system containing oxygen, sulfur or nitrogen atoms;
wherein the carbon atom of the R4 and R5 radicals directly adjacent to the alkoxyamine nitrogen atom is in each case substituted by 3 further organic substituents and
wherein optionally at least one of the radicals R4 and R5 contains a functional group Y which is capable of further reacting or crosslinking with functional groups known in the coatings field;
in a water-containing medium, to form an aqueous phase and nitroxyl radicals,
(2) removing of the aqueous phase and
(3) adding to the nitroxyl radicals one or more monomer(s) of the general formula (III),
HR1C=CR2R3xe2x80x83xe2x80x83(III)
xe2x80x83wherein
R1, R2, R3 are independently selected from the group consisting of: hydrogen, C1-C20alkyl, C1-C20cycloalkyl C6-C24aryl, halogen, cyano, C1-C20alkylester C1-C20cycloalkylester, C1-C20alkylamide, C1-C20cycloalkylamide C6-C24-arylester and C6-C24-arylamide;
as well as
(B) a system which produces free radicals that contains
xe2x80x83(B1) a reducing agent and
xe2x80x83(B2) a molecule able to react with (B1) to form radicals.
The Y group is capable of reacting further or crosslinking and is for example hydroxyl, carboxy, amino, isocyanate, urethane or epoxide groups.
Suitable oxidizing agents (A) are all oxidizing agents known from the prior art for the oxidation of secondary amines into nitroxyl radicals (Rozantsev et al. Synthesis 1971, 4, 192-195). Preferred oxidizing agents are water-soluble oxidizing agents, such as peracids such as peracetic acid, perpropionic acid, m-chloroperbenzoic acid, dimethyldioxirane, perbenzoic acid, or peroxides such as potassium peroxymonosulfate (Oxone(copyright), DuPont Specialty Chemistry, USA), hydrogen peroxide, hydrogen peroxide/sodium tungstate, hydrogen peroxides/titanium containing catalysts, such as for example titanium dioxide and titanium silicalites (EP-A 0 488 403, page 5), phosphotungstic acid and oxidizing gases such as molecular oxygen or ozone. Particularly preferred are peracetic acid, perpropionic acid, m-chloro-perbenzoic acid, Oxone(copyright) (DuPont Specialty Chemistry, USA) and hydrogen peroxide/sodium tungstate.
Metal oxides such as silver oxide, lead (IV) oxide and sodium tungstate may also be used, optionally in combination with another oxidizing agent. A mixture of various oxidizing agents may also be used.
The water-containing medium in which the secondary amine is dispersed may contain a basic organic or inorganic buffer or organic or inorganic bases, such as Na2CO3, NaHCO3, K2CO3, KHCO3, Na3PO4, Na2HPO4, NaH2PO4, metal salts of carboxylic acids such as acetic acid sodium salt or propionic acid sodium salt, or a mixture thereof. Na2CO3, NaHCO3, K2CO3, KHCO3 and the sodium, calcium or potassium salts of acetic acid are preferred.
Useful sterically hindered secondary amines of the general formula (II) are for example those of the following formulare (IV) to (XII): 
wherein
R6, R7, R8,R9,R10,R11,R12,R13, R14,R15,R16, R17, R18, R19 are independently selected from a first group consisting of: hydrogen, halogen or cyano-, amide-, ether-, ester-, thioether-, ketone-, amide-, carbomyl-, amidine- or dialkylphosphonyl-containing groups; or
a second group consisting of: C1-C18alkyl, C2-C18alkenyl, C2-C18alkynyl, C3-C12cycloalkyl or C3-C12heterocycloalkyl, C6-C24aryl, all of which are optionally substituted by NO2, halogen, amino, hydroxy, cyano, carboxy, C1-C4alkoxy, C1-C4alkylthio, C1-C4alkylamino; or
R6 to R19 may form, together with the carbon atom linking them, a C3-C12-cycloalkyl radical, a (C4-C12alkanol)yl radical or a C2-C13hetero-cycloalkyl radical containing oxygen, sulfur or nitrogen atoms;
R6 to R19 together form a residue of a polycyclic ring system or a polycyclic heterocycloaliphatic ring system containing oxygen, sulfur or nitrogen atoms;
wherein optionally at least one of the radicals R6 to R19 contains a functional group Y which is capable of reacting further or of cross-linking with functional groups known in the coatings field and
X represents a methylene, ketone, ester group or oxygen atom, a hydrocarbon radical, which may be substituted by a cyano, nitro, ether, ester, hydroxy or imido group.
Other useful secondary amines are for example those of the following formulae (IX) and (X): 
wherein
R20 is selected from the group consisting of C1-C18alkyl, C2-C18alkenyl, C2-C18alkynyl, C3-C12cycloalkyl, C3-C12heterocycloalkyl and C6-C24aryl, all of which are optionally substituted by NO2, halogen, amino, hydroxy, cyano, carboxy, C1-C4alkoxy, C1-C4alkylthio, C1-C4alkylamino;
R20 may optionally contain a functional group Y which is capable of reacting further or of crosslinking with the functional groups known from the coatings field;
R21, R22 are independently selected from a first group consisting of: hydrogen, halogen or cyano-, amide-, ether-, ester-, thioether-, ketone-, amide-, carbomyl-, amidine- and dialkylphosphonyl-containing groups; and a second
group consisting of: C1-C18alkyl, C2-C18alkenyl, C2-C18alkynyl, C3-C12cycloalkyl, C3-C12heterocycloalkyl, and C6-C24aryl, which are optionally substituted by NO2, halogen, amino, hydroxy, cyano, carboxy, C1-C4alkoxy, C1-C4alkylthio or C1-C4alkylamino;
R21 and R22 optionally form, together with the carbon atom linking them, a C3-C12cycloalkyl radical, a (C4-C12alkanol)yl radical or a C2-C13heterocycloalkyl radical containing oxygen, sulfur or nitrogen atoms; or may together form a residue of a polycyclic ring system or a polycyclic heterocycloaliphatic ring system containing oxygen, sulfur or nitrogen atoms;
wherein R23 and R24 optionally form, together with the phosphorus atom linking them, a C3-C12cycloalkyl radical, a (C4-C12alkanol)yl radical or a C2-C13heterocycloalkyl radical containing oxygen, sulfur or nitrogen atoms;
wherein optionally at least one of the radicals R20 to R24 contains a functional group Y which is capable of further reacting or of crosslinking with functional groups known from the coatings field;
R23, R24 are independently selected from the group consisting of: C1-C18alkyl, C2-C18alkenyl, C2-C18alkynyl, C3-C12cycloalkyl, C3-C12heterocycloalkyl and C6-C24aryl, all of which are optionally substituted by NO2, halogen, amino, hydroxy, cyano, carboxy, C1-C4alkoxy, C1-C4alkylthio or C1-C4 alkyl amino; or
R23 and R24 optionally form, together with the phosphorus atom linking them, a C3-C12cycloalkyl radical, a (C4-C12alkanol)yl radical or a C2-C13heterocycloalkyl radical containing oxygen, sulfur or nitrogen atoms;
wherein at least one of the radicals R23 to R24 optionally contains a functional group Y which is capable of further reacting or of crosslinking with functional groups is known from the coatings field.
Preferred secondary amines of the general formula (II) are tert-butyl amine; 2,2,6,6-tetramethylpiperidine; 4-hydroxy-2,2,6,6-tetramethylpiperidine; 2,2,6,6-tetramethyl-4-piperidinone; 2,2,6,6-tetramethyl-4-piperidinyl acetate; 2,2,6,6-tetramethyl-4-piperidinyl stearate; 2,2,6,6-tetramethyl-4-piperidinyl benzoate; 2,6-dimethyl-2,6-diethylpiperidine; diethyl 1-(tert-butylamino)-2,2-dimethylpropyl-phosphonate; dipropyl 1-(tert-butylamino)-2,2-dimethylpropylphosphonate; dibutyl 1-(tert-butylamino)-2,2-dimethylpropylphosphonate; N-(tert-butyl)-1-(diethylphosphoryl)-2,2-dimethyl-1-propylamine; N-(tert-butyl)-1-(dipropyl-phosphoryl)-2,2-dimethyl-1-propylamine; N-(tert-butyl)-2-methyl-1-phenyl-1-propylamine; 2,2,4,6,6-pentamethyl-1,2,5,6-tetrahydropyrimidine; N-[(3E)-2,2-diphenyl-1,2-dihydro-3H-indol-3-ylidene]-N-phenylamine; 2,6-diethyl-2,3,6-trimethyl-4-piperidinone; 2,6-diethyl-2,3,6-trimethyl-4-piperidinol; 14-oxa-7-azadispiro[5.1.5.2]pentadecane; 2,2,4,4-tetramethyl-1,3-oxazolidine; 2,2,5,5-tetramethyl-1-pyrrolidine; 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidine; 2,5-diphenyl-2,5-dimethylpyrrolidine; 3-carboxy-2,5-diphenyl-2,5-dimethyl-pyrrolidine; 1,1,3,3-tetraethyl-isoindoline; 1,1,3,3-tetramethylisoindoline; 1,1,3,3-tetrapro-pylisoindoline.
Particularly preferred are: tert-butyl amine; 2,2,6,6-tetramethylpiperidine; 4-hydroxy-2,2,6,6-tetramethylpiperidine; 2,2,6,6-tetramethyl-4-piperidinone; 2,2,6,6-tetramethyl-4-piperidinyl acetate; diethyl 1-(tert-butylamino)-2,2-dimethylpropyl phosphonate; dipropyl 1-(tert-butylamino)-2,2-dimethylpropyl phosphonate; dibutyl 1-(tert-butylamino)-2,2-dimethylpropyl phosphonate; 2,6-diethyl-2,3,6-trimethyl-4-piperidinone; 2,6-diethyl-2,3,6-trimethyl-4-piperidinol; 2,2,5,5-tetramethyl-1-pyrrolidine; 1,1,3,3-tetramethylisoindoline.
Polyfunctional amines may also be used as compounds of the formula (II) in order to form resins displaying heat reversibility. In the context of the present invention polyfunctional amines are compounds which have more than one secondary amino group. These properties are particularly interesting when low viscosity of the polymer is required during processing.
Some examples of suitable polyfunctional amines are bis(2,2,6,6-tetramethylpiperidine) sebacate; bis(2,2,6,6-tetramethylpiperidine) succinate; bis(2,2,6,6-tetramethylpiperidine) adipate; bis(2,2,6,6-tetramethylpiperidine) phthalate; bis(2,2,6,6-tetramethylpiperidine) isophthalate; bis(2,2,6,6-tetramethylpiperidine) terephthalate; or polymeric multifunctional amines such as poly((6-((1,1,3,3-tetramethylbutyl)amino)-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidinyl)imino)-1,6-hexanediyl((2,2,6,6-tetramethyl-4-piperidinyl)imino)) (CHIMASSORB(copyright) 944, Ciba Specialty Chemicals, D-Lampertheim).
Typical monoethylenically unsaturated monomers which are suitable for the present invention are the alkyl esters of acrylic or methacrylic acids, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and isobutyl methacrylate; the hydroxyalkyl esters of acrylic or methacrylic acids, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate; acrylamide, methacrylamide, N-tertiary butylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide; acrylonitrile, methacrylonitrile, allyl alcohol, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, phosphoethyl methacrylate, N-vinylpyrrolidone, N-vinylformamide, N-vinylimidazole, vinyl acetate, conjugated dienes such as butadiene or isoprene, styrene, styrenesulfonic acid salts, vinylsulfonic acid salts and 2-acrylamido-2-methylpropane-sulfonic acid salts and acryloyl. Also suitable are cis- and trans-stilbene and diphenylethylene.
Examples of comonomers suitable for use in the present invention are C3-C6-ethylenically unsaturated monocarboxylic acids as well as the alkali metal salts and ammonium salts thereof. The C3-C6-ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid and acryloxypropionic acid. Acrylic acid and methacrylic acid are the preferred monoethylenically unsaturated monocarboxylic acid monomers.
Examples of C8-C16-ethylenically unsaturated phenolic compounds which may also be used as comonomers are 4-hydroxy styrene, 4-hydroxy, xcex1-methyl styrene, 2,6-ditert-butyl and 4-vinyl phenol.
Another class of carboxylic acid monomers suitable for use as comonomers in this invention are C4-C6-ethylenically unsaturated dicarboxylic acids and the alkali metal and ammonium salts thereof as well as the anhydrides of cis-dicarboxylic acids. Suitable examples include maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid and citraconic acid. Maleic anhydride (and itaconic acid) is the preferred monoethylenically unsaturated dicarboxylic acid monomer(s).
The acid monomers suitable for use in the present invention may be in the form of their acids or in the form of the alkali metal salts or ammonium salts of the acid.
Preferred monomers are selected from the group consisting of (meth)acrylic acid esters of C1-C20-alcohols, acrylonitrile, cyanoacrylic acid esters of C1-C20-alcohols, maleic acid diesters of C1-C6-alcohols, maleic anhydride, vinyl-pyridines, vinyl(alkylpyrroles), vinyloxazoles, vinyloxazolines, vinylthiazoles, vinylimidazoles, vinylpyrimidines, vinyl ketones, styrene or styrene derivatives which contain a C1-C6-alkyl radical or halogen in the xcex1-position and contain up to 3 additional substituents on the aromatic ring. Nonpolymerizable vinyl monomers such as cis- and trans-stilbene, and diphenylethylene are also preferred.
Particularly preferred monomers are methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, iso-bornyl methacrylate, maleic anhydride, styrene or acrylonitrile.
The compound (B1) is a reducing agent, such as for example transition metal compounds, sulfur compounds of a low degree oxidation or compounds which may be readily enolized. Preferred are sodium hydrogen sulfite, reducing sugars such as a glucose and dextrose, carbonyl compounds which may be readily enolized, such as ascorbic acid and hydroxyacetone, and metal ions, such as Fe2+, Ti3+ and Cu1+. Particularly preferred are Fe2+, Ti3+ and Cu1+ in the form of inorganic salts or organic salts.
Component (B2) is a molecule able to react with (B1) to form one or more free radicals. Hydrogen peroxide is preferably employed as component (B2) in the context of the present invention.
Hydrogen peroxide is a thermodynamically metastable compound in the form of the pure substance and in aqueous solution (e.g. 30% perhydrol). The rate of dissociation of hydrogen peroxide is greatly increased, even at room temperature, by catalysts, (e.g. finely divided metals, manganese dioxide, dust particles, non-metal ions, such as Ixe2x88x92, IO3xe2x88x92 and OH31 , or metal ions, such as Fe2+, Fe3+ and Cu2+). Hydroxyl radicals may be generated in a controlled manner from hydrogen peroxide by thermal decomposition of the hydrogen peroxide or by one-electron redox reactions of the hydrogen peroxide with a suitable electron donor. Typical compounds are for example sodium hydrogen sulfite, carbonyl compounds which may be readily enolized, such as ascorbic acid and hydroxyacetone, and metal ions, such as Fe2+, Ti3+ and Cu1+. The reaction of Fe2+ with hydrogen peroxide to give hydroxyl radicals which may be used for oxidation of organic compounds has become known by the name of Fenton""s reagent. The hydroxyl anion formed in the redox reaction may also initiate the peroxide dissociation.
In the process according to the invention for the preparation of an alkoxyarnine initiator of the formula (I), an hydroxyl radical (generated from H2O2 and reducing agent B1) adds on to a Cxe2x95x90C double bond of the monomer of the general formula (III) thus introducing the hydroxyl group into the monomer of the general formula (III) which is then reacted with the nitroxyl radical to form the alkoxyamine initiator (I).
In principle, other compounds of the type Rxe2x80x2xe2x80x94Oxe2x80x94Oxe2x80x94Rxe2x80x3 may also be used as component (B2). The radicals Rxe2x80x2 and Rxe2x80x3 may contain a functional group Y which is capable of further reacting or of crosslinking with the functional groups known from the coatings field, for example OH, NH2, NHR or epoxide.
One way of carrying out the invention is that in the first step the secondary amine of formula (II) is introduced into a reaction vessel containing water-containing medium. The weight ratio of water to secondary amine is in the range of about 0.1 to 200, preferably about 1 to 50, and more preferably about 2 to 30. It is preferred that the water contains a basic inorganic or organic buffer or inorganic or organic bases. The molar ratio of secondary amine to buffer or base is in the range from about 20 to 0.05, preferably about 10 to 0.1, more preferably about 5 to 0.5.
Preferably the secondary amine of formula (II) is dissolved in a suitable solvent that is immiscible in water, in order to form a biphasic medium. Preferred solvents are toluene, xylene or dichloromethane. The solvent to secondary amine weight ratio is in the range from about 0.1 to 30, preferably about 0.5 to 10, and more preferably about 1 to 5.
While stirring vigorously, the oxidizing agent (A) is then slowly added in its pure form to the reaction vessel containing the secondary amine of formula (II). It is also possible to add a solution of the oxidizing agent (A) to the reaction vessel. Suitable solvents used for that purpose are inert towards the various reagents and do not react during the reaction: they are for example toluene, xylene, dichloromethane. When the oxidizing agent (A) is water-soluble, the preferred solvent is water. The solvent to oxidizing agent weight ratio is in the range from about 0.1 to 30, preferably about 0.5 to 10, and more preferably about 1 to 5.
With certain functional groups (e.g. Yxe2x95x90NH2), it may be advantageous to provide the functional groups with a protective group during the reaction described (e.g. protection of amino groups as acetamides; Later liberation of the amido function by hydrolysis with a base); for Yxe2x95x90OH, however, it is not necessary to use protective groups.
The temperature of the reaction may range from about xe2x88x9210xc2x0 C. to about 100xc2x0 C., preferably about 0xc2x0 C. to 80xc2x0 C., and more preferably about 0xc2x0 C. to 40xc2x0 C. The reaction time may range from about 10 minutes to about 72 h, preferably about 1 h to 36 h, and more preferably about 2 h to 24 h. The first step of the process of the present invention may be carried out in air or in an inert gas atmosphere such as nitrogen or argon.
In the second step, after the partial or complete oxidation of the secondary amine to form a nitroxyl radical, stirring is terminated and the aqueous phase is removed.
In the third step, the vinyl monomer of formula (III), component (B1) and optionally some additional solvents are added to the organic phase of step two. Suitable solvents for the third step of the process are water, alcohols, preferably methanol, ethanol or isopropanol, ethers, preferably diethylether, oligoethylene glycols or THF, carbonyl compounds, preferably acetaldehyde, acetone or methyl ethyl ketone, or any desired mixtures of the solvents mentioned. While stirring component (B2) is slowly metered in. It is therefore possible to add component (B2) in the form of an aqueous solution.
Component (B2) is used a 0.1- to 20-fold molar excess based on the initial secondary amine. Component (B1) is used in an equimolar amount, but preferably in an up to 20% molar excess, based on the secondary amine initially introduced. The vinyl monomer of formula (III) is used in a 0.2- to 20-fold molar excess, based on the secondary amine initially introduced. The reaction temperature may range from about xe2x88x9210xc2x0 C. to 150xc2x0 C., preferably 0xc2x0 C. to 100xc2x0 C., and more preferably 25xc2x0 C. to 60xc2x0 C. The reaction may be carried out in air or in an inert gas atmosphere, preferably in an inert gas atmosphere such as in nitrogen or argon. The pH of the reaction solution may optionally be adjusted to a range from 5 to 7 with substances such as NaHCO3.
After the reaction is complete, the solution may be optionally filtered in order to remove any solid residue such as iron(III) salts. The residual monomer of formula (III), solvents and oxidizing agent (A), if volatile, are removed in vacuo. An organic solvent not miscible with water is added and the organic phase is washed with acidic water (pH≈5-2) in order to remove the residual secondary amine. Optionally, the organic phase may be washed with basic water (pH≈7.5-9.5) and/or reducing agents, in order to remove excess oxidizing agent. The organic phase is then dried under a drying agent such as Na2SO4 or MgSO4. The elimination of the solvent under vacuum provides the crude alkoxyamines of the formula (I).
Another object of the present invention is to provide a new process for preparing oligomers, cooligomers, polymers or block or random copolymers, which comprises preparing the functional alkoxyamines of formula (I) according to the process of the present invention and adding at least one polymerizable monomer to the unpurified alkoxyamine of formula (I) followed by heating.
An important advantage of the process according to the present invention is that an additional purification step of the alkoxyamines may be dispensed with.
For the preparation of the (co)polymers according to the present invention, all the components such as monomer(s), crude alkoxyamine of the formula (I) are reacted at a temperature ranging from about 0xc2x0 C. to 260xc2x0 C., preferably about 50xc2x0 C. to 200xc2x0 C., and more preferably about 70xc2x0 C. to 150xc2x0 C., for a period of time ranging from about 30 minutes to 72 hours, preferably about 1 hour to 48 hours, more preferably about 2 hours to 24 hours. The polymerization is carried out in an inert gas atmosphere, for example nitrogen or argon.
Optionally, some additives may be added to the polymerization medium before the polymerization or during the polymerization process in order to accelerate the polymerization. Such additives are well-known in the art and are for example camphorsulfonic acid, 2-fluoro-1-methylpyridinium p-toluenesulfonate, acylating compounds such as acetic anhydride (Tetrahedron 1997, 53(45), 15225), glucose, dextrose (Macromolecules 1998, 31, 7559), ascorbic acid (Macromolecules 2001, 34, 6531) or long-life radical initiators as reported in U.S. Pat. No. 6,288,186 (column 4, lines 8-24).
Suitable monomers are the water-soluble and water-insoluble polymerizable monomers mentioned above.
The (co)polymers of the present invention may have a number average molecular weight of from 1000 to 2xc2x7106, preferably from 2000 to 5xc2x7105, more preferably from 2000 to 2.5xc2x7105.
The alkoxyamine compound of the formula (I) is introduced in a quantity ranging from about 20 wt % to 0.01 wt %, preferably 10 wt % to 0.05 wt % and more preferably 5 wt % to 0.1 wt %, based on the weight of the monomer(s).
Preferably for the preparation of the (co)polymers only small amounts of organic solvents are used. If organic solvents are required, suitable solvents or mixtures of solvents are typically pure alkanes such as hexane, heptane or cycloalkane, carbonyl compounds such as methyl ethyl ketone, hydro-carbones such as benzene, toluene or xylene, halogenated hydrocarbons such as chlorobenzene, esters such as ethyl acetate, propyl, butyl or hexyl acetate, ethers such as diethyl ether, dibutyl ether or ethylene glycol dimethyl ether, alcohols such as methanol, ethanol, ethylene glycol or monomethyl ether or mixtures thereof of them. The solvent to monomer weight ratio is in the range from about 0 to 5, preferably from about 0 to 2.
The type of polymerization used may be bulk, solution, emulsion, dispersion or suspension polymerization and it may be carried out both batchwise and continuously.
The polymers prepared according to this invention show a low polydispersity (Mw/Mn) which is usually lower than 2 and may be significantly lower.
The number average molecular weight of the polymer chains increases linearly with the monomer conversion, which allows a tailor-made polymer molecular weight to be obtained. Furthermore, the molecular weight of the polymers may be controlled by varying the amount of crude alkoxyamine compared to the amount of monomers. High molecular weight polymers may be formed.
A further advantage of the present invention is that after the removal of the non-polymerized monomers from the (co)polymers or after reaching a conversion rate of 100%, a second polymerization step may be initiated simply by adding to the polymer synthesized in the first step a portion of fresh vinyl monomer or monomer mixture that may be different from the vinyl monomer or monomer mixture used in the first polymerization step. The polymerization of the vinyl monomer or monomer mixture added in the second step is then initiated by the polymer chains synthesized in the first polymerization step and di-block copolymers may be for example produced if the polymer chains synthesized in the first polymerization step consists of linear chains with one single growing chain end. The molecular weight and polydispersity of each block may be controlled independently during the respective polymerization step. This process may be repeated several times and may then provide multiblock copolymers of controlled molecular weight and molecular weight distribution for each block.
The resulting polymers are usually colorless and they may be used in most cases without any further purification.